Tube fitting for stainless steel tubing

Abstract

A tube fitting that uses only two components, namely a fitting body and a fitting nut. The nut and body are adapted to be threadably coupled together by relative rotation therebetween. The nut includes an integral tube gripping ring that cooperates with a camming surface on the body when the fitting is made-up. The camming surface preferably has a steep camming angle. The ring is radially compressed against the tube outer wall to form a seal and a tight tube grip. The ring also forms a line contact-type seal against the camming surface. The ring is designed to have a hinging action and to plastically deform during pull-up to embed into the tubing for excellent tube grip, and an axially adjacent swage or collet zone that isolates any stress riser resulting from the embedding action from vibration effects. The fitting components, and particularly the ring, may be case hardened, the fitting may include a self-gauging feature to indicate sufficient pull-up to prevent excessive pull-up. Also provided is a single ferrule tube fitting that uses a steep camming surface and is at least about 3.3 times harder than the stainless steel tube end.

1. A tube fitting, comprising:
 a body and nut that are joinable; said body having an interior bore that is adapted to receive a tube end along a longitudinal axis of the fitting; said bore having a camming surface at one end of said bore; 
 said nut having an interior shoulder that forms a drive surface; and 
 a ferrule having a front end and a back end; said ferrule back end engaging said nut drive surface when the fitting is pulled up; said ferrule front end engaging said camming surface during pull-up to provide a seal; said ferrule front end plastically deforming and having a front edge that is configured to bite into the tube end when the tube fitting is pulled up on the tube end; said nut when joined to said body driving said ferrule against said camming surface; 
 wherein said camming surface forms an included angle of at least thirty-five degrees to about sixty degrees with respect to said longitudinal axis; and 
 wherein said ferrule back end is radially spaced from the tube end after a completed pull-up of the fitting. 
 
   
   
     2. The tube fitting of  claim 1  wherein when the tube fitting is pulled up on the tube end, said ferrule plastically deforms with a hinging action that produces a radial compression in a central portion of said ferrule against said tube end to swage said ferrule onto the tube end. 
   
   
     3. The tube fitting of  claim 1  wherein said ferrule has a cylindrical interior bore at said front end and a circumferential recess formed in said interior bore and axially spaced from said front end. 
   
   
     4. The tube fitting of  claim 1  wherein when the tube fitting is pulled up on the tube end, said ferrule front end indents into an outer surface of the tube end to form a shoulder that contacts said front end; said ferrule having a substantially cylindrical interior bore portion that is adjacent said front end; said bore portion being radially compressed against the tube end upon completing an initial pull-up of the fitting. 
   
   
     5. The fitting of  claim 1  wherein said camming angle is about 45°. 
   
   
     6. The tube fitting of  claim 1  wherein the nut and the body are stainless steel. 
   
   
     7. The fitting of  claim 1  wherein said ferrule is case hardened over part of its surface. 
   
   
     8. The fitting of  claim 1  wherein said ferrule back end forms a convex ferrule driven surface that engages said nut drive surface. 
   
   
     9. The fitting of  claim 1  wherein said ferrule comprises an axially tapered outer wall that joins said ferrule front end to said ferrule back end. 
   
   
     10. A tube fitting, comprising:
 a body and nut that are joinable; said body having an interior bore that is adapted to receive a tube end along a longitudinal axis of the fitting; said bore having a camming surface at one end of said bore; 
 said nut having a drive surface; and 
 a ferrule having a front end and a back end; said ferrule back end engaging said nut drive surface when the fitting is pulled up; said ferrule front end engaging said camming surface during pull-up to provide a seal; wherein said ferrule has a cylindrical interior bore that extends from said ferrule front end to said ferrule back end and a circumferential recess formed in said interior bore and axially spaced from said front end; said ferrule front end plastically deforming and having a front edge that indents into the tube end when the tube fitting is pulled up on the tube end; said nut when joined to said body driving said ferrule against said camming surface; 
 wherein said camming surface forms an included angle of at least thirty-five degrees to about sixty degrees with respect to said longitudinal axis. 
 
   
   
     11. The tube fitting of  claim 10  wherein when the tube fitting is pulled up on the tube end, said ferrule plastically deforms with a hinging action that produces a radial compression in a central portion of said ferrule against said tube end to swage said ferrule onto the tube end. 
   
   
     12. The fitting of  claim 11  wherein said ferrule has an outer wall with a concavity that facilitates the radial compression of a central portion of the ferrule. 
   
   
     13. The fitting of  claim 10  wherein said camming angle is about 45°. 
   
   
     14. The tube fitting of  claim 10  wherein when said ferrule front edge indents into the tube end, a shoulder is formed on the tube that contacts said front end of the ferrule, said ferrule having a substantially cylindrical interior bore portion that is adjacent said front end; said bore portion being radially compressed against the tube end upon completing an initial pull-up of the fitting. 
   
   
     15. The tube fitting of  claim 10  wherein said ferrule back end is radially spaced from the tube end after a completed pull-up of the fitting. 
   
   
     16. A tube fitting, comprising:
 a body and nut that are joinable; said body having an interior bore that is adapted to receive a tube end along a longitudinal axis of the fitting; said bore having a camming surface at one end of said bore; 
 said nut having an interior shoulder that forms a drive surface; and 
 a ferrule having a front end and a back end; said ferrule back end engaging said nut drive surface when the fitting is pulled up; said ferrule front end engaging said camming surface during pull-up to provide a seal; said ferrule front end having a front edge configured to bite into an outer surface of the tube end when the tube fitting is pulled up on the tube end; said nut, when joined to said body, driving said ferrule against said camming surface; 
 wherein upon fitting pull up with the tube end, a portion of said ferrule body located between said ferrule front end and said ferrule back end is radially compressed against said tube end to swage said ferrule against said tube end; 
 wherein said camming surface forms an included angle of at least thirty-five degrees to about sixty degrees with respect to said longitudinal axis; and 
 wherein said ferrule has an outer wall with a concavity that facilitates the radial compression of a portion of the ferrule. 
 
   
   
     17. The tube fitting of  claim 16  wherein the portion of the ferrule being radially compressed against said tube end is produced by a hinging action of said front end of said ferrule during pull-up. 
   
   
     18. The tube fitting of  claim 16  wherein the nut and the body are stainless steel and said ferrule is case hardened over part of its surface. 
   
   
     19. A tube fitting, comprising:
 a body and nut that are joinable; said body having an interior bore that is adapted to receive a tube end along a longitudinal axis of the fitting; said bore having a camming surface at one end of said bore; 
 said nut having an interior shoulder that forms a drive surface; and 
 a ferrule having a front end and a back end; said ferrule back end engaging said nut drive surface when the fitting is pulled up; said ferrule front end engaging said camming surface during pull-up to provide a seal; said ferrule front end plastically deforming and having a front edge that is configured to bite into the tube end when the tube fitting is pulled up on the tube end; said nut when joined to said body driving said ferrule against said camming surface; 
 wherein said camming surface forms an included angle of at least thirty-five degrees to about sixty degrees with respect to said longitudinal axis; and 
 wherein said ferrule back end forms a convex ferrule driven surface that engages said nut drive surface.